Field of the Invention
The invention relates to a method for initializing an anti-theft system for a motor vehicle. The anti-theft system has a transceiver unit disposed in the motor vehicle that transmits interrogation signals via an antenna. The interrogation signals are received by a portable response transmitter which in turn responds by transmitting a response signal back to the transceiver. The transceiver in turn evaluates the response signal.
A known anti-theft system has an antenna device in the driver's door and is described in Published, Non-Prosecuted German Patent Application DE 38 20 248 A1. If a user wishes to get into the vehicle, an interrogation/response dialog is triggered by activating a trigger circuit. In the process, an interrogation signal is transmitted by the antenna device in the vehicle to a response transmitter carried by the user. The response transmitter transmits back an encrypted response signal if it receives the interrogation signal. In the motor vehicle, the response signal is compared with an expected setpoint signal and if the two correspond (successful authentication), the doors are locked or unlocked.
The same interrogation/response dialog also takes place in the motor vehicle when the user wishes to start the vehicle. After the ignition switch is activated, an interrogation signal is emitted and a response signal is subsequently transmitted back. If the response signal is authorized, the immobilizer is deactivated.
In such an anti-theft system, the range of the interrogation signal may be too low, so that the response transmitter cannot receive the interrogation signal. The range of the interrogation signal may also be too large and other response transmitters located in the vicinity may be addressed in error (overshoot). When attempting to release the immobilizer it is particularly important that only one response transmitter in the vicinity of the vehicle or in the interior of the vehicle is addressed, even if the response transmitter is stored, for example, far from the ignition lock in the side compartment in the interior of the vehicle. If the response transmitter cannot receive the interrogation signal, the user cannot get into his motor vehicle and cannot start his motor vehicle either.